This application is a National Phase Application (35 USC 371) of PCT/JP99/06385 filed Nov. 16, 1999 and claims priority of Japanese Application No. 11-132857 filed May 13, 1999.
The present invention relates to a scanning tunneling microscope, a probe for use with the scanning tunneling microscope, a method of treating the probe, and a method of fabricating a nano-structure.
Conventional techniques in pertinent technical fields are disclosed in, for example, the papers listed below.
(1) H. J. Mamin, P. H. Guethner, and D. Rugar: Phys. Rev. Lett. 65 (1990) 2418.
(2) C. S. Chang, W. B. Su, and Tien T. Tsong: Phys. Rev. Lett. 72 (1994) 574.
(3) M. Takai, H. Andoh, H. Miyazaki, and T. Tsuruhara: Microelectronic Engineering 35 (1997) 353.
Among several proposed methods for fabricating nano-structures by use of an STM (scanning tunneling microscope), the following is closest to the present invention.
In many cases, the term STM stands for an apparatus for observation of a surface nano-structure on a conductive substrate which is performed by bringing a conductive probe close to the substrate so that the distance between the probe and the substrate becomes about 1 nanometer, and the voltage applied between or current flowing between the probe and the substrate is controlled and measured in order to observe the surface nano-structure. However, in the present invention, the term STM stands not only for an apparatus adapted for observation of a surface nano-structure on a substrate through measurement and control of voltage applied between or tunnel current flowing between a probe and the substrate, but also an apparatus adapted for micro-machining of the surface of a probe or a substrate through utilization of the effects of voltage applied between and tunnel current flowing between the probe and the substrate.
FIG. 1 is a schematic view showing such a conventional scanning tunneling microscope and the principle of a method of fabricating a nano-structure by use of the scanning tunneling microscope.
As shown in FIG. 1, a thin wire made of a metal used for fabrication of a structure is used as an STM probe 101. Voltage and tunnel current are applied between the STM probe 101 and a substrate 102. Through the effects of the voltage and, metal atoms 103 are transferred from the tip end of the STM probe 101 onto the substrate 102, resulting the formation of a nano-structure. Reference numeral 100 denotes a three-dimensional drive unit.
Further, a thin wire 111 which is made of a metal and which is coated with another metal 112 as shown in FIG. 2 has also been used as an STM probe 110. In this case as well, voltage and tunnel current are applied between the STM probe 110 and a substrate, and through the effects of the voltage and tunnel current, metal atoms are transferred from the tip end of the STM probe 110 onto the substrate, resulting the formation of a nano-structure.
However, when these conventional methods are used, atoms of a material metal are transferred intermittently onto a substrate in the form of clusters, or only a few metal atoms are transferred continuously onto the substrate. In other words, continuous supply of metal atoms from a probe to a substrate has been difficult to attain.
Therefore, it is difficult for the conventional method to fabricate a continuous nano-structure.
In view of the above-described problem, an object of the present invention is to provide a scanning tunneling microscope, a probe for use with the scanning tunneling microscope, a method of treating the probe, and a method of fabricating a nano-structure, which facilitate formation of a micro-structure.
In order to achieve the above object, the present invention provides:
[1] A scanning tunneling microscope characterized by being equipped with a probe formed of a mixed-conductive material having both ion conductivity and electron conductivity.
[2] A scanning tunneling microscope described in [1] above, characterized in that the mixed-conductive material is an Ag2S crystal.
[3] A scanning tunneling microscope described in [1] above, characterized in that the probe has a projection (mini chip) which is provided on the tip end of the mixed-conductive material and is grown or contracted through application of voltage and tunnel current between the probe and a substrate.
[4] A method of treating a probe for a scanning tunneling microscope comprising the steps of: preparing a probe for a scanning tunneling microscope formed of a mixed-conductive material having both ion conductivity and electron conductivity; applying voltage and tunnel current between the probe and a substrate in order to move movable metal ions within the mixed-conductive material to thereby grow on the tip end of the probe a projection (mini chip) composed of the metal ions (atoms); and reversing the polarity of the applied voltage after the growth of the projection in order to return the metal ions (atoms) constituting the grown projection (mini chip) into the mixed-conductive material to thereby contract the projection.
[5] A method of treating a probe for a scanning tunneling microscope described in [4] above, characterized in that an Ag2S crystal is used as the mixed-conductive material.
[6] A method of observing a nano-structure on the surface of a substrate, characterized in that voltage and tunnel current are applied between the substrate and a probe for a scanning tunneling microscope treated by the method described in [4] or [5] above.
[7] A method of fabricating a nano-structure by use of a probe for a scanning tunneling microscope formed of a mixed-conductive material having both ion conductivity and electron conductivity, characterized in that, through application of voltage and tunnel current between the probe and a substrate, a surface micro structure of the substrate is observed, and movable ions or atoms of the mixed-conductive material are transferred onto the surface of the substrate to thereby fabricate a nano-structure.
[8] A method of fabricating a nano-structure by use of a probe for a scanning tunneling microscope formed of a mixed-conductive material having both ion conductivity and electron conductivity, characterized in that, through application of voltage and tunnel current between the probe and a substrate, movable ions or atoms of the mixed-conductive material are transferred onto the substrate to thereby fabricate a nano-structure on the substrate.